Forty-four patients with idiopathic, intractable pruritus ani were randomly assigned to receive, in double-blind fashion, topical capsaicin (0.006%) or placebo (menthol 1%) ointment for four weeks. After a one-week washout period, each patient received the alternate treatment for an additional four weeks. The ointment was prepared by diluting Zostrix® (0.025%) in white soft paraffin. The treatment was applied in a very thin layer to the perianal area, three times a day. Prior to the study, a pilot study was performed on five patients, to determine which of two concentrations of capsaicin (0.012% or 0.006%) had the best profile of effectiveness and side effects. At the end of the controlled study, responders from both groups continued capsaicin in open-label fashion. Thirty-one (70%) of 44 patients experienced relief during capsaicin treatment and did not respond to menthol; all patients not responding to capsaicin also failed to respond to menthol (p < 0.0001). The mean pruritus score improved by approximately 60% in the group as a whole during capsaicin treatment. The beneficial effect was immediate in 24 patients and occurred within 3 days in 7 patients. Four patients discontinued treatment because of side effects (perianal burning in 3, urticaria in 1). All patients had some perianal burning following each capsaicin application; this decreased significantly after four weeks of application, but did not disappear completely. During a mean follow-up period 10.9 months, 29 responders needed to apply capsaicin a mean of every 1.6 days (range 0.5-7 days) to remain symptom-free or nearly symptom-free.

Comment: Pruritus ani is a common problem characterized by an intense urge to scratch around the anal area. Causes include persistent moisture around the anus from excessive sweating, sensitivity to various foods and beverages, fungal infection, and skin diseases such as eczema or psoriasis. In many cases, the cause of the problem cannot be identified, and attempts to treat it are unsuccessful. The results of the present study indicate that capsaicin, a substance found in cayenne pepper, is a safe and highly effective treatment for severe intractable idiopathic pruritus ani. While the mechanism by which capsaicin relieves pruritus ani is not entirely clear, it may work by depleting from the skin a chemical messenger known as substance P that plays a role in the perception of itching.

Lysy J, et al. Topical capsaicin - a novel and effective treatment for idiopathic intractable pruritus ani: a randomised, placebo controlled, crossover study. Gut 2003;52:1323-1326.